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Resistance to Flow on a Sloping Channel Covered by Dense Vegetation following a Dam Break
Author(s) -
Melis Mattia,
Poggi Davide,
Fasanella Giovanni, Oscar Domenico,
Cordero Silvia,
Katul Gabriel G.
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr023889
Subject(s) - drag , mechanics , drag coefficient , flume , turbulence , flow (mathematics) , hydraulic roughness , rod , boundary layer , constant (computer programming) , geometry , geology , surface finish , wavefront , physics , geotechnical engineering , mathematics , materials science , optics , medicine , alternative medicine , pathology , computer science , composite material , programming language
The effect of hydraulic resistance on the downstream evolution of the water surface profile h in a sloping channel covered by a uniform dense rod canopy following the instantaneous collapse of a dam was examined using flume experiments. Near the head of the advancing wavefront, where h meets the rods, the conventional picture of a turbulent boundary layer was contrasted to a distributed drag force representation. The details of the boundary layer around the rod and any interferences between rods were lumped into a drag coefficient C d . The study demonstrated the following: In the absence of a canopy, the Ritter solution agreed well with the measurements. When the canopy was represented by an equivalent wall friction as common when employing Manning's formula with constant roughness, it was possible to match the measured wavefront speed but not the precise shape of the water surface profile. However, upon adopting a distributed drag force with a constant C d , the agreement between measured and modeled h was quite satisfactory at all positions and times. The measurements and model calculations suggested that the shape of h near the wavefront was quasilinear with longitudinal distance for a constant C d . The computed constant C d (≈0.4) was surprisingly much smaller than the C d (≈1) reported in uniform flow experiments with staggered cylinders for the same element Reynolds number. This finding suggested that drag reduction mechanisms associated with unsteadiness, nonuniformity, transient waves, and other flow disturbances were more likely to play a role when compared to conventional sheltering effects.